Experimenting with UV-‐sensitive Beads

Experimenting with UV-‐sensitive Beads By Deborah Scherrer, Stanford Solar Center Participants experiment with ultraviolet (UV) light-‐sensitive plastic beads, which are generally white but turn colors when exposed to UV light. •
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Materials Needed: 5 UV-‐sensitive beads per participant 1 pipe cleaner or ribbon per participant 1 worksheet per participant Materials such as water, sunscreen, orange pill bottles, sunglasses, fabric, etc. for experimentation (see worksheet) 1 bookmark sheet per participant (optional) Heavy paper or manila folders, glue, scissors (optional) Imagery of EM spectrum and SDO (optional) UV (“black”) light or flashlight if sunlight is not available Activity Time: ~30 minutes Age Group: 7 -‐ adult1 Target audience: Public science education events, youth groups, scientists visiting classrooms, other informal science settings. Can be used to introduce the concept of UV or EUV invisible light prior to lectures on NASA missions that utilize UV light. May be adapted to classrooms 2-‐12. Learner Objectives: After the activity, students/participants should understand that: 1. The Sun produces light in all wavelengths, including invisible ultraviolet (UV) 2. UV can be dangerous and can burn our skin, damage our eyes, and destroy our cells. 3. The Earth’s atmosphere provides significant, but not complete, protection from UV. 4. There are both ways to detect UV and also to protect ourselves from it. 1 The beads are attractive to younger children, however it is difficult for them to understand the concept of invisible light. The beads should NOT be given to children under 3 because of the possibility of choking. Stanford University Solar Center 1 Obtaining UV beads: You can purchase UV beads from Educational Innovations™ or a similar source: http://www.teachersource.com/LightAndColor/Ultraviolet/UltravioletDetectingBeads.asp When gathering beads, 1 large coffee scoop holds ~75 beads. Warm temperatures help the beads change from white to colored. Cool temperatures, e.g. ice water, help the beads return quickly to white. Note: Some older sunscreens do not work with these beads, nor do they work with human skin. Newer sunscreens have corrected this deficiency. Background: These beads contain a special chemical that changes color when exposed to ultraviolet (UV) light. UV is an invisible type of light from the Sun. It can burn our skin and cause cancer, damage our eyes, and destroy our cells. Most UV is blocked by our Earth’s ozone layer and atmosphere, but some still gets through and can be detected. The beads will stay white when inside or not exposed to UV. Incandescent and fluorescent lights will not affect them. They will only turn bright colors when exposed to UV, usually from the Sun or a UV (“black”) light. The darker the color of the beads, the more UV rays they are detecting. Once you bring the beads back indoors, they will (slowly) change to white again. This process can be repeated many times. (Further information on UV is provided with the EM spectrum image.) Process: 1. Paraphrase the description above and show participants the electromagnetic spectrum chart. Ask them if they understand that there are more forms of light than what we can see. Can they give examples [X-‐ray, radio waves, etc.]? Reinforce the concept that ultraviolet (UV) is a form of light that cannot be detected by our eyes but is emitted by the Sun and other stars. 2. Hand out beads and pipe cleaners, and bookmark materials if you wish to make them. Have participants assemble their bookmark, if necessary. Then have the students string their beads onto the pipe cleaner or ribbon, put it through the hole in the bookmark, and twist or tie the ends together. 3. Now, ask the students to be the scientist and experiment with their beads! Hand out the worksheets and have participants determine which materials keep the beads, and hence themselves, safe from dangerous UV, and which materials don’t. Have them test their beads with the various items on the worksheet – do they look white, faint, or colored? Can they think of other items to test? Stanford University Solar Center 2 4. Final discussion: Ask students which of the materials tested are most effective at keeping you safe from dangerous UV light from the Sun? As a reflection closer, ask students at what times of the day are they most at risk for UV radiation from the Sun? [mid-‐day] Least at risk? [night, sunrise, sunset]. In which season are they most at risk? [summer] Do not tell students the answers. Let them go home thinking about them. Going Farther: Show students the images following or current images from NASA’S SDO/AIA, TRACE, IRIS, STEREO, or other missions taking imagery in UV. Ask students why the images are unusually colored. [They were taken in UV, which is invisible to human eyes, so computers have colored the data to make them visible.] What wavelengths of light cause a color change in the UV beads? Infrared 1000-‐700 nm Visible 390-‐700 nm UV-‐A 400-‐315 nm UV-‐B 315-‐280 nm UV-‐C 280-‐100 nm Infrared light makes our skin feel warm and can be detected some animals such as snakes. Visible light can be seen by our eyes. It includes all the colors of the visible rainbow. Too much exposure to ultraviolet A can results in the same damage as UV-‐B but to a lesser degree. Ultraviolet B light is needed for vitamin D synthesis in our bodies, but is a major cause of sunburn, skin cancer, cataracts, suppression of the immune systems, and photo-‐aging. Ultraviolet C light is extremely dangerous, but completely absorbed by the ozone in the Earth’s atmosphere and does not reach the Earth’s surface. Beads are white >360 nm Beads are colors 360-‐300 nm Beads are white 300 – 100 nm Descriptive information from Educational Innovations Stanford University Solar Center 3 You be the scientist! UV bead worksheet Your prediction Actual Color of Beads Safe from UV? Notes Under water In sunlight Using sunscreen Cloudy sky (Do you think the beads will be white, faint, or colored?) (i.e. no direct sunlight) Behind paper Behind sun glasses Behind eye glasses Under cloth Inside plastic orange medication bottle Behind window glass Behind car windshield In shade or under brim of cap Behind plastic Sun at mid-‐day Sun at sunset/sunrise UV (black) light Fluorescent light Incandescent light LED light (white, faint, or colored) Stanford University Solar Center 4 The Electromagnetic Spectrum and Ultraviolet Light Ultraviolet (UV) light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-‐rays (in the range between 400 nm and 10 nm). It is so-‐named because the spectrum consists of electromagnetic waves with frequencies higher than those that humans identify as the color violet. UV frequencies are invisible to humans, but near UV is visible to a number of insects and birds. Although ultraviolet radiation is invisible to the human eye, most people are aware of the effects of UV on the skin, like suntan and sunburn. Short-‐wavelength and mid-‐wavelength UV can cause much damage to living organisms, such that life on Earth outside of the deep oceans is possible only because the atmosphere, primarily the ozone layer, filters out nearly all short-‐wavelength and most mid-‐range UV. A small amount of UV reaches the surface and is capable of causing long-‐
term skin damage and cancer. A smaller amount of UV reaches the surface and is responsible for sunburn and also the formation of vitamin D in humans. Thus UV light has many effects, both beneficial and damaging, to human health.2 2 This, and more information, is available from Wikipedia and the web. Stanford University Solar Center 5 UV Bead Bookmarks Stanford and Lockheed Martin Solar and Astrophysics Lab developed these bookmarks to support this lesson. The bookmarks briefly explain the electromagnetic spectrum and UV light. To assemble bookmarks: • Make copies of the patterns here. • Have students cut them out and fold in half lengthwise. • Cut a piece of cardstock the same size as the bookmark, fold the bookmark around the cardstock, and glue. • Punch a hole in the top. Stanford University Solar Center 6 The Sun in UV light NASA/SDO AIA instrument (images taken in EUV but artificially colored) In astronomy, very hot objects preferentially emit UV radiation. Our Sun primarily emits UV in the areas above the surface and in the Sun’s extremely hot atmosphere (“corona”). This area is where most intense solar activity occurs. Because the ozone layer blocks many UV frequencies from reaching telescopes on the surface of the Earth, most UV or EUV (extreme ultraviolet) observations are made from space. The Sun seen in UV by human eyes (it’s invisible) NASA’s SDO/AIA instrument NASA’s SDO/EVE instrument (spectrograph images) Stanford University Solar Center NASA’s TRACE mission NASA’s IRIS mission NASA’s STEREO mission 7 PROB2/SWAP NASA’s SDO/AIA instrument ESA/NASA’s SOHO/EIT instrument NASA’s SDO/SAM instrument NASA’s SDO/AIA instrument (black dot is Venus transiting the Sun) NASA’s TRACE mission Extremely hot stars emit proportionally more UV radiation than the Sun. Our Sun’s emissions peak in the visible light range, hence our eyes have evolved to see visible light. Beings on planets where their star’s emission peaks in the UV would have different eyes than ours, ones sensitive to UV, and perhaps they would see their world differently than humans do. To the right is an artist’s conception of what such a star and planet might look like. Stanford University Solar Center 8

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